The present invention relates generally to rectifiers and more particularly to Schottky barrier rectifying devices, and methods of forming these devices.
Power devices typically include an active region and a termination region at the periphery of the active region to prevent premature voltage breakdown. Conventional termination structures include local oxidation of silicon (LOCOS), field plate, guard ring, or a combination thereof. Because large electric fields can arise in the vicinity of the LOCOS, a significant leakage current may flow through leakage paths in the termination region. A conventional approach to reducing such leakage currents is shown in FIG. 1.
FIG. 1 shows a substrate 12 on which a trench Schottky rectifier is formed. The device includes an active region 5 and a termination region 10. The semiconductor substrate 12 has a first conductivity type, typically N-type conductivity, on which an epitaxial layer 20 is formed. Epitaxial layer 20 is also of the first conductivity type and more lightly doped than substrate 12. A series of trenches 30 are formed in the active region 5 of the device. The trenches are lined with a gate oxide layer 25 and filled with doped polysilicon. The polysilicon filled trenches 30 are continuously connected over the surface of the structure. A LOCOS region 40 is formed in the termination region 10 to isolate the active region 5 from the termination region 10. The LOCOS region 40 extends to the boundary defining the active region 5 and the termination region 10.
A p+ doped region 50 is formed below LOCOS region 40 by ion implantation and diffusion. Doped region 50 enhances the reverse-biased voltage so that pinch-off is maintained in the termination region 10, thus eliminating a path through which leakage current can be conducted. A metal anode layer 55 is formed over the exposed surfaces of the polysilicon-filled trenches 30 and epitaxial layer 20 in the active region 5 and over the LOCOS region 40 in the termination region.
Unfortunately, the device shown in FIG. 1 is relatively complex and expensive to manufacture because three lithographic masking steps are involved. Specifically, a separate masking step is required to form the trenches, p+doped region, and contacts.
Accordingly, it would be desirable to provide a structure for a trench Schottky diode in which premature voltage breakdown arising from leakage currents is avoided and which can be manufactured with less than three lithographic masking steps.